Many forming techniques have been developed for fabricating inorganic powders into useful shapes. Typical techniques used in the industry include slip casting, tape casting, isostatic pressing, extrusion, roll compacting and the like. These processes typically include dispersion of the powder in a solvent medium, use of an organic binder to hold the article together during and after the forming process, thermally decomposing the binder and sintering the article.
There are many difficulties with previously practiced techniques for fabricating inorganic powders. For instance, when dispersing the powder in the solvent medium, if the powder is not uniformly dispersed, then the undispersed powder agglomerates. The undispersed powder causes voids in the sintered article. The binder must also be uniformly dispersed due to similar effects. Generally, it is difficult to uniformly disperse the inorganic powder and binder in the solvent medium.
Another problem with the previously practiced technique is that it is also difficult and expensive to remove the solvent medium. Typically, for roll-compacted substrates, water is removed by an expensive spray drying process. For organic-based tape casting processes, the solvent is removed by heated air, then recovered in an expensive solvent recovery system.
More in particular, difficulties arise if the powder, binder and other ingredients are dry blended. For instance, when the binder is dry blended with the inorganic powder, and water is added to form a slurry, the dry ingredients are incompletely dispersed in the slurry. The resulting article, after sintering, has large variations in density and porosity due to the incomplete dispersion of the powder and/or binder in the slurry mixture. Another blending technique practiced in the industry is to externally solubilize the binder in water and then to add the inorganic powder to the solution. The use of this technique results in the need to add additional water, which in turn reduces the total percent solids of the slurry, causing the mixture to have an undesirable pseudoplastic flow characteristics.
In view of the prior art, it would be desirable to provide a method for homogeneously dispersing an inorganic powder and a thermally gelling polymeric binder in a solvent medium without negatively affecting the pseudoplastic flow of the mixture. It would also be desirable to have an inexpensive process to rapidly remove the solvent medium from a formed article.